1. Field of the Invention
The present invention is directed to a vehicle brake support assembly for an internally expanding drum brake assembly and, more specifically, to a vehicle axle and brake support assembly for a drum brake which is utilized in heavy duty trucks and trailers and usually includes a pair of dual web brake shoes and a rotary cam actuator.
2. Description of the Prior Art
Such brakes usually include a pair of brake shoes having adjacent ends seated for pivotal movement on a cylindrical surface of a pair of anchor pins mounted to a support plate, often referred to as a "spider" which in turn is secured to a vehicle axle or axle housing. The support plate is usually of elongate form and a rotatable actuating cam and shaft is mounted to the support plate at the end opposite the anchor pins with the cam disposed between the other ends of the brake shoes. During actuation, rotary movement of the cam causes each of the brake shoes to overcome the biasing force of a return spring and to pivot outwardly about the anchor pins into contact with the radially inwardly facing friction surface of a brake drum secured for rotation with a vehicle wheel.
For such heavy duty brake installations, the support plate or spider serves as the foundation of the brake assembly and, even though it does not constitute a moving part of the brake assembly, it is subject to and must withstand substantial stress under dynamic braking conditions. In this type of brake the rotary cam shaft is usually rotatably mounted to the support plate at a location spaced inwardly from a plane normal to the vehicle axle and passing through the center of the brake shoes and anchor pins. The support plate is therefore subject to substantial twisting forces as it transfers braking torque to the axle under dynamic braking conditions.
Support plates have therefore traditionally been formed as heavy cast and/or forged members with appropriate areas machined and bored to accommodate the anchor pins and the actuating shaft, and for mounting the support plate to the axle. Such traditional support plates have therefore been expensive to manufacture because of the mass of metal and the machining operations required and increased the weight of the vehicles thereby reducing the economics of operation thereof. Examples of such heavy duty cast and forged support plates or spiders are disclosed in U.S. Pat. Nos. 3,144,100, 3,279,569, 3,363,726, and 4,157,747.
Several attempts have been made to avoid the massive cast and forged brake spiders. U.S. Pat. Nos. 3,385,405, and 4,452,347 disclose the use of two plates secured together to provide a brake support assembly. U.S. Pat. Nos. 4,200,174 and 4,337,851 each disclose the use of a stamped brake spider or support plate.